Treatment of cellulosic fibers



March 1956 c. F. ENGSTROM ETAL 2,739,091

TREATMENT OF CELLUL'OSIC FIBERS Filed June 17, 1952 ,from other naturally occurring cellulosic .fibers.

United States Patent TREATMENT on CELLULOSIC FIBERS Carl .F. Engstrom and Ignatius A. the Boston, Detroit, Mich., assignors to United States Rubber Company, New York,jN.'Y., a corporation of New Jersey Application June 17, 1952, Serial No. 293,996

11 Claims. (Cl. 154-90) This invention relates to an improved method of "treatingnaturally occurring cellulosic fibers to improve their tensile-strength and more particularly to such amethod which is an improvement over the method disclosed in -U. S. patent to H. M. Buckwalter No. 2,297,536.

The Buckwalter patent covers the treatment of-native cellulosic fibers with non-volatile, non-waxy, water-solu- Me, cotton-wax-peptizing agents which contain a tricyclic hydroaromatic condensed nucleus, particularly withaqueous solutions of alkali salts of rosin acids, to improve the'tensile strength thereof.

The naturally occurring waxes in the native cellulosic fibers to which the present invention is applied, such :as

. cord is subjected to tension, the cotton'waxes .behave .as

lubricants allowing the fibers to slip over each othermore readily. This lubricating action is thought to account for the relatively low tensile strength of cord made of untreated grey cotton containing the original naturally occurring waxes. The lubricating action of such waxes is also thought to explain the increase .in tens'ilestreng'th brought about when such cord is extracted with .hot alcohol to remove these cotton waxes.

Alcohol extraction of the naturally occurring waxes from grey cotton or similar naturally occurring cellulosic fibers is not commerciallypractical. However, the afore- ..mentioned.Buckwalter patent is based upon the discovery of a commercially practical method of greatlyincreasing the tensile strength of grey cotton cord and cord made This method involves treating the grey cotton cord or the like 'with a water solution of a material typified bysodium rosinate, whereby an appreciable gain in tensile strength .results. Experiments .have shown that thecotton cords need not be immersed for long periods of time,.i mmersion times .as short .as five seconds being sufiicient to effect thetensile improvement. This fact suggests the possibility that in this type of treatment :the cotton -.WflXS .or similar .n-aurally occurring waxes are not removed but -are;-merely peptized. However, experirnentalistudiesihave indicated that it is not enough forarnaterial to be zapeptiz:

ling agent but it mustalso be a de-plasticizing agentfwith respect to the waxesif it-is to efiect the desired improvement in tensile strength. Most'common pepti-zingegents :are plasticizing agents for the waxes and .therefore are However, :the alkali :saltsvalueless .as tensile virnprovers.

In the rosinate or'the like maintained "at constant level.

2,739,091 Patented I Mar. 20, 1956 of rosin acids, e. g., sodium rosinate, are both dep'lasticizing and =peptizing agents for the cotton waxes or likewaxes. It appears therefore that the success of the process disclosed in the Buckwalter patent is due'to the fact that the naturally occurring waxes act as lubricants in cords made from the naturally occurring cellulosic fibers and that water solutions of alkali salts of rosin acids serve to both peptize and 'de-plasticize'these-waxes, thus 'detroying their lubrication actionwith a. resulting increase in' tensile strength.

In the commercialpractice of the invention described in the 'Buckwalterpatent, a plurality of the grey cotton cords or the like, disposed in parallel relationship, are passed through a tank of aqueous solution of .sodium The concentration of sodium rosinate or other alkali salt of a rosin acid typically "is in the range of 7.0 to 8.5% by weight. Passage of the cords through such .a solution serves'to impregnate them thoroughly with the sodium rosinate. Wetting and complete saturationof thecords with the'solution take place almost instantaneously. From the treating tank the cords pass through squeeze rolls which are.so.located .that the squeezed-out solution .falls back into the tank to be re-used. Upon leaving the squeeze rolls the cords pass through a counter-flow wash tank in Which'they are thoroughly washed with water which serves to remove surplus treating solution. Fresh 'waterIis continuously introduced at the rearof the washing tank and continuously overflows at the front. The motion of the cords isirom the front to the rear Ofz'thfi washing tank. The thustreated cords typically are then solutioned with an aqueous mixture comprising rub- .ber in the form .cfulatex, with or without ;a dissolved resorcinol-formaldehyde resin, after which the solutioned cords are assembled with unvulcanized rubber into reinforced rubber articles, e. g., a pneumatic tire, and the rubberarti'cles are then vulcanized in the conventional manner.

Buc'kwalter process it has been found that periodic' blow- In the above-described commercial operation of the ing or blistering occurred during the curing of articles of rubberxreinforced with cords which had been treated by the Buckwalter procedure. This blowing or blistering is extremely serious and causes an unduly high-number of rejects, thereby greatly increasing the cost of production. Exhaustive investigation indicated that this blisteringor blowing was attributable to the maintenance of the flow of wash water at too high a rate with the result that 'the concentration of sodium rosinate in the wash =Water fell to such alow level as to permit hydrolysis of sodium rosinate to occur to a substantial degree in accordance with the following Equation 1:

The ,rosin acid thereby formed transferred to the-cords and insome manner caused blowing of the rubberarticles during vulcanization.

.Etlorts were made to overcome this .diificulty byso controlling the flow of wash water throughthe washing tank as to keep the concentration of sodium rosinate in the wash water above a certain minimum level, typically above by weight. However, even after the direct relation between hydrolysis of sodium rosinate in the washing operation and the occurrence of blowing-during vulcanization was established andetforts were made to control'it'by maintaining the concentration of sodium rosinate in the wash water above the minimum leveltby .;reducing the flow of wash water through :the washing tank, there still occurred what might be termed epidernics of blowing or blistering during vulcanizationland efforts sto find the cause of this werefruitless for .adong 3 time. cause of such epidemics of blowing during cure and our discovery of a simple and commercially feasible method of completely preventing the same.

The accompanying drawing portrays diagrammatically one arrangement of apparatus for practicing the method of our invention.

After great difiiculty and much experimentation, We have traced the occurrence of blowing during vulcanization of rubber articles reinforced with cotton or like cords treated by the above-described Buckwalter process to the following facts: (1) the cotton cords selectively absorb a substantial amount of alkali as they pass through the wash water and this absorption results in depletion of the wash water in alkila and lowering of the pH; and (2) the pH of the wash water as it enters the Washing tank is at a rather low level, typically about 7. We have found that occasionally, due to operating variables, these two factors become accumulative to such a degree as to permit the hydrolysis reaction described above to 'occur despite maintenance of the concentration of the alkali salt of the rosin acid in the wash water above a minimum value. As previously indicated, the occurrence of this hydrolysis reaction in some as yet unexplained manner causes blistering of the tires or other rubber articles during vulcanization.

We have further found that these difficulties can be overcome in a simple, economical and commercially feasible manner by simply maintaining the hydrogen ion concentration of the wash water at a value not greater than the value for Cn+ given by the following Equation 2:

(2) Kw-Ka where CH+ is hydrogen ion concentration, Kw is the ionization constant of water (in dilute solutions and at ordinary temperature the ionic productcan be assumed to be and is assigned a value of 10", Ka is the ionization constant of the rosin acid and C is the concentration of the alkali salt of the rosin acid in the wash water. We prefer to maintain the hydrogen ion concentration of the wash water substantially below the value calculated for Cn+, in order to provide an adequate margin of safety. Typically, we maintain the wash water at a pH value equal to at least 0.5 above the pH value corresponding to the calculated value for Cn-k.

In the typical practice of our invention, we simply dissolve, an any suitable way, an alkali, especially an alkali metal hydroxide, in the incoming wash water before it comes into contact with the impregnated grey cotton or like fibers, introducing such an amount of alkali as to keep the hydrogen ion concentration from exceeding the value for Crr-las determined by the above Equation 2. We typically prepare a water solution of the alkali to be added and meter this solution, which usually is of relatively low strength, say 1% by weight, in accurately controlled proportions into admixture with the incoming wash water in such manner that a completely homogeneous solution is obtained before the wash water enters the washing tank. Example Following is a working example of a typical method of operating in accordance with our invention. Sodium rosinate is used in aqueous solution in accordance with the following formulation to treat grey cotton cords. The treating solution has the following formulation:

.Dresinate XX" (Sodium rosinate-made by Hercules Our invention is based upon our discovery of the 4 The caustic soda is added to 400 gallons of water. The mixture is agitated and heated to the boiling point. Then the Dresinate XX is added with constant agitation. The mixture is held at about 205 F. for at least 15 minutes after which water is added in amount such as to bring the volume of the solution to 1,000 gallons. The solution is maintained at a temperature of 165 15.15" F. while the cords are being passed through it. The kerosene is added not over 5 minutes before the solution is to be used. The kerosene serves as an antifoam to minimize foaming which would otherwise normally occur to an excessive extent in the handling of the sodium rosinate solution.

Since abietic acid, which is the principal acid in rosin, is a very weak acid, the value for Ka for it being 3.14 X 10* and since it is highly insoluble in water, it precipitates as it is formed and causes the equilibrium indicated by the above Equation 1 to be shifted to the right. The pH at which the equilibrium occurs is calculated by the use of the above expression for the hydrogen ion concentration where Kw has a value of 10*, as stated above, Ka has a value of 3.14 X 10- and C is the concentration of sodium rosinate in the wash water. Since, in ordinary commercial operation, the concentration of sodium rosinate in the wash water is approximately 1%, the value of C can be assumed to be 0.031 moles of sodium rosinate per liter. Substituting in the above Equation 2 and performing the calculation, the hydrogen ion concentration at the point at which equilibrium would occur is found to be 10- This value was found to correspond closely to the value obtained in practice on the wash water in which the products of hydrolysis began to appear at pH values of 9 and under.

Applying our invention, sodium hydroxide or other suitable alkali is dissolved in the wash water in an amount such as to always maintain the hydrogen ion concentration at not over l0 Actually, for safety, we prefer to add alkali in such amount as to maintain the hydrogen ion concentration substantially below 1O typically at not over 10- (which corresponds to a pH of at least 9.5), and still more preferably at a value not greater than 10- (i. e., at a pH of 10 or over). Assuming that the pH of the available wash Water is 7, the amount of sodium hydroxide necessary to raise its pH to 10 is calculated to be 1.6 grams per gallons of wash water. This neglects the above-mentioned absorption effects of the cotton cord, but in actual practice it has been found that the addition of the above amount of sodium hydroxide will give a pH (in the wash water in the wash tank) in the range of 9.5 to 9.6 which is considered to be a quite safe operating range since the danger point is 9. The specitied amount of alkali (1.6 grams of sodium hydroxide per 100 gallons of incoming wash water) is conveniently added in the form of a 1% solution by means of a metering pump to the fresh, typically demineralized,

water before it enters the wash tank so as to form a completely uniform washing liquid free from Stratification or localized spots of high or low concentration.

In the drawing, a web 1 of parallelly disposed grey cotton cords enters treating tank 2 which contains an aqueous solution of sodium rosinate or other alkali salt of a rosin acid. This solution is replenished via inlet 3. Web 1 is guided through the aqueous solution by rolls 4 and is thoroughly impregnated with the treating solution in tank 2. The web 1 then passes upwardly through a pair of rubber-covered squeeze rolls 5 which squeeze out excess solution which runs back into tank 2. The web 1 then passes around guide rolls 6, thence into wash tank 7 through which the web is guided by rolls 8, and thence through a pair of rubber-covered squeeze rolls 9 which squeeze out excess aqueous material. The web then goes to latex solutioning means or any other subsequent treating means (not shown).

Fresh wash water is continuously introduced into wash tank 7 via inlet 10 and continuously overflows via/outlet 5 11, after traversing tank 7 counter-currently to the cords.

In accordance with our invention a dilute (say 1%) solution of sodium hydroxide or other suitable alkali in water is placed in supply tank 12 and is fed continuously at an accurately controlled rate by means of pipe 13, metering pump 14, and pipe 15 into admixture with the incoming wash water, e. g., demineralized water, entering the system via pipe 16. I

Normally we operate in such a way that the concentration of sodium rosinate or other alkali salt of a rosin acid in the water in the wash tank ranges from 1.0 to 2.0%.

It will be seen that we are not limited to operation with any particular level of sodium rosinate or the like in the wash water since the above expression takes into account variations in this concentration. Similarly although our invention is usually applied with an alkali metal salt of ordinary rosin, we are not limited thereto since if other rosin acids are used as the basis of the salt used to improve the tensile strength of the grey cotton cord or the like, the appropriate ionization constant for such acid will simply be substituted in the above expression.

Similarly, we are not limited to the use of sodium hydroxide as a means of maintaining the desired pH in the wash water in the washing tank. We can use any other alkali metal hydroxide although potassium hydroxide is the only one of these that is cheap enough to be considered. Instead of an alkali metal hydroxide, we can use any other water-soluble alkaline material capable of maintaining the desired pH in the wash water provided such alkaline material is not objectionable in the finished cord. Examples of such other alkaline materials include ammonium hydroxide and water-soluble organic amines, e. g., alkanolamines such as triethanolamine and diethanolamine, alkyl amines and quaternary ammonium hydroxides, e. g., trimethylbenzyl ammonium hydroxide, etc.

The invention is of special utility in connection with the production of tire cord from which rubberized fabric plies are made, which in turn become part of the pneumatic tire carcass. By reason of the improved tensile strength of the unrubberized tire cord, it is possible to make a standard quality tire with less tire cord, or in the alternative to make a superior tire with the usual quantity of tire cord. The chemically treated grey cotton cords may, with or without intermediate drying, be immersed in a rubber latex composition for the making of weftless cord fabric for tire carcasses. The latex composition, when dry, ultimately acts to bind the cords in parallel relation.

The invention may be applied to treating finished tire cords made of grey cotton, or to grey cotton fibers in any form as for example, yarn, plied yarn, cabled yarns, twisted products from plied yarns, fabrics woven from yarns or cords, unspun cotton, etc. It will be understood that reference herein to cords is intended to include'treatment of a single cord or a plurality of cords disposed in parallel relationship to form a sheet or web.

While rubberizing of the treated cotton has been referred to above as illustrative of further processing, it will be apparent that various uses of the grey cotton will not require rubberizing and the production of unrubberized fabrics including the treated cotton is within the scope of the invention.

The rosin acid, the alkali salt of which is u sedinthe initial treating solution, is usually ordinary rosin (which is mainly abietic acid-either wood or gum rosin can be used), but it can be any of the rosin acids found in ordinary rosin such as pure or substantially pure abietic acid, d-pimaric acid, or sapinic acid, or it can be a modified rosin, i. e., rosin which has been chemically modified to change the rosin nucleus, e. g., heat treated rosin, isomerized rosin, polymerized rosin, hydrogenated rosin, disproportionated rosin, etc. The rosin acid can be pure or substantially pure dehydroabietic acid, tetrahydroabietic acid or dihydroabietic acid.

The term "rosin acid is used herein in a generic sense to include the isomeric abietic .acid, sapinic acid, and d-pimaric acid which occur in varying amounts in wood and gum rosins of different geographical origins, also the heat treated, isomerized, polymerized, hydrogenated, disproportionated and dehydrogenated derivatives of such acids, and also the content of such acids and derivatives in tall oils, disproportionated tall oils and refined tall oils.

The material which. is combined with the rosin acid, replacing the hydrogen of the carboxylic acid group thereof, is usually an alkali metal, especially sodium or potassium. However, it can be the ammonium group or it can be the group resulting from neutralization of the rosin acid with an organic amine such as an alkanolamine, an alkylamine, or a quaternary ammonium hydroxide.

From the foregoing description many advantages of our invention will be apparent to those skilled in the art. The principal advantage is that the invention provides a simple, easily applied, economical, commercially feasible, and highly effective method of preventing the occurrence of blowing or blistering during vulcanization of rubber articles reinforced with grey cotton or like fibers which have been treated by the above-mentioned Buckwalter process as commercially practiced. Another advantage is that use of our invention requires but little added expense in the way of chemicals, equipment and control. Another advantage is that our invention makes it unnecessary to maintain any minimum value for the concentration of sodium rosinate or the like in the wash water, such as is referred to above, although in actual practice we usually operate with a concentration of sodium rosinate or the like in the wash water of from 1.0 to 2.0%.

Having thus described our invention, what we claim and desire to protect by Letters Patent is:

1. In a process of improving the tensile strength of naturally occurring cellulosic fibers containing at least 75 of the original naturally occurring waxes by impregnating said fibers with an aqueous solution of an alkali salt of a rosin acid, removing excess solution from the impregnated fibers and then washing the impregnated fibers with water flowing countercurrently to the impregnated fibers, the improvement which comprises maintaining the hydrogen ion concentration of the wash water at a value substantially below the value for Cn given by the equation Kw-Ka 's-l- C where CH-I- is hydrogen ion concentration, Kw is the ionization constant of water and is taken as equal'to 10- Ka is the ionization constant of said rosin acid, and C is the concentration of said salt in the wash water, by dissolving alkali in the wash water prior to'contact thereof with said impregnated fibers, said alkali being selected from the group consisting of alkali metal hydroxides, ammonium hydroxide, and water-soluble organic amines.

2. In a process of improving the tensile strength of naturally occurring cellulosic fibers containing at least 75% of the original naturally occurring waxes by impregnating said fibers with an aqueous solution of sodium rosinate, removing excess solution from the impregnated fibers and then washing the impregnated fibers with water flowing 'countercurrently to the impregnated fibers, the improvement which comprises maintaining the hydrogen ion concentration of the wash water at a value substantially below the value for 011+ given by equation 05+ KwKa 7 hydroxide in said .wash waterprior to contact thereof .with said impregnated fibers.

*3. 'In a :process iof improving 'the tensile strength -:of naturally occurring icellulosic fibers containing at 18381. 75% :of the original naturally occurring waxes by impregnating said fibers withran aqueous solution-of sodium rosinate :removing excess :solution from the :impregnated fiberszandtthen washing the impregnated fibers with water fiowirrgcountercurrently :to the impregnated fibers-under suchconditions that the concentration of sodium rosinate in said wash water is approximately 1%, the improvement whichcomprises maintaining the hydrogen ion con centration .ofrsaid twash waterat a value substantially 'below 10- tbytdissolvingzsodium hydroxide in said wash water prior to contact ."thereof :with said impregnated fibers.

4. .A process as settforth in claim 33 wherein the amount of-said sodium hydroxide is such asto maintain the hydrogen ion concentration of said wash water at a value not greater than 1'0". 7

'5. sIn a process of :improving the tensile strength of grey cottontcontaining at least 75% of the original naturallyoccurring waxes by impregnating. said grey cotton .with:an aqueous solution of an alkali metal salt of a rosin acid, remaining.solution from the impregnated grey cotton andthen washingtheimpregnated fibers with water flowing countercurrently to the impregnated grey cotton, the improvement-which comprises maintaining the hydrogen ion concentration of the wash water at a value substantially below the value for (311+ given by the equation GB wC-IKa where .CH-iis hydrogen ion concentration, Kw is the ionization constant of .water and is taken 'as equal to 10- Ka is the ionization constant of said rosin acid, andLCis the concentration of'said salt in the washxwater, by dissolving alkalimetal hydroxide-in said wash water prior to contact with said impregnated fibers.

.6. .A process as :set 'forth in .claim '5 wherein the hydrogen ion concentration of said wash water is maintained at a;levelcorrespondingioapH .value at*1east0.5 greater than the pH value corresponding to the value for Car-,- given by said equation.

7. In a process of improving the tensile strength of grey cotton containing at least 75% of the original natturally occurring waxes rby impregnating said grey cotton .with an aqueous solution of :sodiumr-rosinate, :rernoving excess solution from ;the impregnated ,fibers and then washing .the impregnated fibers with water flowing counter-currentlywith respect thereto under such condi tions that the concentration :of sodium rosinate in the washwater is approximately 1% the improvement which gen "ion :concentration of said wash *water -'is maintained at a level :corresponding' to a pH -valueat' least'u5 greater than'the pH value corresponding to the value for='Ga'-|- given by said equation.

10. In a'process of making -vulcanized rubber articles reinforced :with cords made from naturally occurring cellulosic'fiberscontaining at least of the original naturally occurring waxes by impregnating said cords withan aqueous solution ofan alkali salt of a 'rosin acid, removing excess solution "from the impregnated "cords by squeezing and thereafter washing the impregnated cords with water fiowingcountercurrently to the impregnated cords, asseniblingihe resulting cords with unvulcanized rubber to form'rubber articles reinforced with said cords, and vulcanizirrg the resulting rubber articles, the improvement which comprises eliminating'blowing or blistering during the vulcanization of said articles by maintaining the hydrogen ion concentration of said wash water at-=a value substantially below the value for 011+ given by the equation where Cn-lis hydrogen ion "concentration, Kw is the ionization constant of water andis taken asequal'to 10*, Kn is the ionization constant of-said rosin acid, andCis the concentration of-said salt in the wash water, -by dissolving'alkali in the wash water prior to contactthereo'f withsa'id impregnatedcords, said alkali being selected "from the group consisting of alkali -metal hydroxides, ammonium hydroxide, 'andwater-soluble organic amines.

H. in 'a process of makingvulcanized'rubberarticles reinforced with grey cotton cords containing at least 75% 'of the-original naturally occurring waxes by impregnating said cords with an aqueous solution of sodium-rosinate, removing excess solution from the impregnated cordsby squeezing and thereafter-washing the impregnated cords 'With water "flowing 'countercurrently to the impregnated cords, assembling 'the -resulting cords with unvulcanized rubber to form-rubber articles'reinforced with said cords, and'vulcanizing the resulting rubber articles,-the improvement which-comprises eliminating blowing or'blistering during the vulcanization of said articles by maintaining the'hydrogen' ion concentration of said wash wa'terat a level corresponding-toapH *value'at' least 0.5 greaterthan the-pH valuecorresponding'tothevalue for Ctr-1- given 'bythe'equation K -K CH+= Where iCn-lis hydrogen ion concentration, Kw is the ionization constant of 'water and is taken as equal to References Cited in theme of this patent UNITED ,STATES PATENTS 2,297,636 Bnckwalters .....rSept. 29, 1942 2,429,397 Compton .Qcta2l, .1947

,2,5.02;406 IEntwistle Mar. 128, 1950 

10. IN A PROCESS OF MAKING VULCANIZED RUBBER ARTICLES REINFORCED WITH CORDS MADE FROM NATURALLY OCCURING CELLULOSIC FIBERS CONTAINING AT LEAST 75% OF THE ORIGINAL NATURALLY OCCURING WAXES BY IMPREGNATING SAID CORDS WITH AN AQUEOUS SOLUTION OF AN ALKALI SALT OF A ROSIN ACID, REMOVING EXCESS SOLUTION FROM THE IMPREGNATED CORDS BY SQUEEZING AND THEREAFTER WASHING THE IMPRIGNATED CORDS WITH WATER FLOWING COUNTERCURRENTLY TO THE IMPREGNATED CORDS, ASSEMBLING THE RESULTING CORDS WITH UNVULCANIZED RUBBBER TO FORM RUBBER ARTICLES REINFORCED WITH SAID CORDS, AND VULCANIZING THE RESULTING RUBBER ARTICLES, THE IMPROVEMENT WHICH COMPRISES ELIMINATING BLOWING OR BLISTERING DURING THE VULCANIZATION OF SAID ARTICLES BY MAINTAINING THE HYDROGEN ION CONCENTRATION OF SAID WASH WATER AT A VALUE SUBSTANTIALLY BELOW THE VALUE FOR CH+ GIVEN BY THE EQUATION 